1. Field of the Invention
The present invention generally relates to fluid sampling systems and particularly to such systems having a plurality of different sample probes which are selectively connectable to a fluid analyzer.
2. Description of the Prior Art
Fluids moving in ducts and pipes with no obstructions have laminar flow if the Reynolds Number is less than 2,000. Under such conditions stratification of the fluid occurs across the duct or pipe area. Thus, a sample taken at one point in the duct may be of considerably different composition than a sample taken at another point in the duct.
In order to obtain a representative sample of the fluid passing through the duct or pipe, it is known to insert sample probes at various points across the duct. Examples of such a placement of sample probes at different points in the duct may be found in U.S. Pat. No. 3,736,792 issued June 5, 1973 to Stephen D. Poulsen and U.S. Pat. No. 3,780,566 issued Dec. 25, 1973 to Kenneth Burton Smith et al. In such known set-ups although the diameters of the sample probes are approximately equal and equal volumes of fluid enter the sample probes, since the distance from the inlet of the sample probe to the exhaust of the probe are not equal thorough sampling for averaging purposes is not accomplished since the fluid entering the farthest inlet of the sample probes will not reach the outlet of that sample probe at the same time as fluid entering the shorter inlet to outlet sample probes. Therefore, the composite of the fluids exhausted from the various sample probes is not a true representation of the fluid flowing across the pipe at any given instant and does not provide a true average of such.
The diameters of the various probes could be sized so that the fluid transport times from each sample probe would be equal. However, then the volume of fluid entering eachsample probe would not be equal and the composite sample from all the probes would again not be a true average but would be biased towards the fluid entering the larger diameter probes. An example of such a system using variable diameter inlets may be found in U.S. Pat. No. 3,777,571 issued Dec. 11, 1973 to Erich Jaeger.